Henry Gellibrand

Henry Gellibrand (1597 to 1637) was an English mathematician best known for his work on the Earth's magnetic field. In 1635 he announced that magnetic declination, the angle between a compass needle and true north, is not constant but changes over time, a result he drew from earlier observations that had not yet been correctly interpreted. He also devised a method of finding longitude from eclipses, and in 1633 he published the mathematical tables of Henry Briggs as Trigonometria Britannica. He succeeded Edmund Gunter as professor at Gresham College in 1626. He was the son of the physician Henry Gellibrand, and he was buried in the London church of St Peter le Poer, which was demolished in 1907.